Antenna coupling element, antenna device, and electronic device

ABSTRACT

An antenna device includes first and second radiating elements, and an antenna coupling element. The antenna coupling element includes a primary coil electrically connected between the first radiating element and a feed circuit and a secondary coil inductively coupled to the primary coil and electrically connected between the second radiating element and a ground. A capacitor is provided between the primary coil and the secondary coil, thus causing current to flow from the primary coil to the secondary coil or the second radiating element via the capacitor even at an anti-resonant frequency of the first radiating element.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to Japanese PatentApplication No. 2017-141549 filed on Jul. 21, 2017 and is a ContinuationApplication of PCT Application No. PCT/JP2018/021580 filed on Jun. 5,2018. The entire contents of each application are hereby incorporatedherein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to an antenna coupling element that isused in an electronic device including an antenna, an antenna deviceincluding the antenna coupling element, and an electronic deviceincluding the antenna coupling element.

2. Description of the Related Art

In recent years, wider bandwidths of frequency bands used forcommunication have been proceeding. With high integration of electronicdevices including a communication device, there is no margin space forantennas, and many antennas cannot be provided to cover multiplefrequency bands. Because of these situations, the need for antennashaving wideband characteristics has been increasing.

As one method of providing a wideband antenna, a technique for addingthe characteristics of a passive radiating element physically separatedfrom a feed circuit to the characteristics of a feed radiating elementby coupling the passive radiating element to the feed radiating elementwith a magnetic field is used.

FIG. 8 is an equivalent circuit diagram of an antenna device including afeed radiating element and a passive radiating element that are coupledto each other with a magnetic field. In this way, in the antenna deviceincluding the passive radiating element, first, the feed radiatingelement is fed with power from a feed circuit 1, and the passiveradiating element is coupled to the feed radiating element with amagnetic field.

For example, International Publication No. 2012/153690 describes anantenna device. The antenna device includes two radiating elements and acoupling adjustment circuit that controls power to be fed to the tworadiating elements.

To provide an antenna device with a wider bandwidth, a feed radiatingelement is often used for a fundamental resonant mode and a 3λ/4harmonic resonant mode. FIG. 9A shows the frequency characteristics ofan antenna device in which a passive radiating element is further addedto a feed radiating element. The abscissa axis represents frequency, andthe ordinate axis represents a return loss (S11) of the antenna deviceviewed from a feed circuit. In FIG. 9A, resonant points (poles) appearat frequencies fo, fh, fs. The frequency fo is a fundamental (λ/4)resonant frequency of the feed radiating element, and the frequency fhis a harmonic (3λ/4) resonant frequency of the feed radiating element.The frequency fs is a resonant frequency of the passive radiatingelement.

When the resonant frequency fs of the passive radiating element isbrought close to the harmonic resonant frequency fh of the feedradiating element, a wideband antenna device that uses the frequency foas a low band and uses a wide frequency band including the frequency fsand the frequency fh as a high band is formed.

The feed radiating element also has an anti-resonant mode in which thefeed radiating element resonates at λ/2 (the electrical length of anantenna is λ/2). The anti-resonant frequency is a frequency between thefundamental resonant frequency fo and the harmonic resonant frequencyfh. In the anti-resonant mode, the feed radiating element viewed fromthe feed circuit is open in terms of impedance, so no current flowsthough the feed radiating element.

However, the above-described magnetic field coupling between the feedradiating element and the passive radiating element occurs as a resultof flow of current through the feed radiating element, so current isrequired to flow through the feed radiating element for the antennadevice to exhibit predetermined characteristics. Therefore, magneticfield coupling does not occur at the anti-resonant frequency at which nocurrent flows through the feed radiating element.

FIG. 9B shows a graph for a further wideband device in which the lengthof the passive radiating element is extended and the resonant frequencyof the passive radiating element is decreased, as compared to the caseshown in FIG. 9A. However, in the example shown in FIG. 9B, the resonantfrequency fs of the passive radiating element coincides with theanti-resonant frequency fa. Accordingly, the passive radiating elementis not coupled to the feed radiating element, and the resonantcharacteristics of the passive radiating element do not appear. In otherwords, a wideband effect is not obtained from provision of the passiveradiating element.

SUMMARY OF THE INVENTION

Preferred embodiments of the present invention provide antenna couplingelements that each enable effective use of resonance of a passiveradiating element by overcoming a problem due to anti-resonance of afeed radiating element and that enables a wider bandwidth in a widefrequency band, and antenna devices and electronic devices, includingthe antenna coupling element.

An antenna coupling element according to a preferred embodiment of thepresent invention includes a first coil, and a second coil coupled tothe first coil. A first end of the first coil is a feed circuitconnection end. A second end of the first coil is a feed radiatingelement connection end. A first end of the second coil is a passiveradiating element connection end. A second end of the second coil is aground connection end. A winding direction of the first coil that isrouted along a current path from the feed circuit connection end to thefeed radiating element connection end and a winding direction of thesecond coil that is routed along a current path from the secondradiating element connection end to the ground connection end areopposite to each other.

With the above features, current flowing through the first coil betweenthe feed circuit and the first radiating element flows through thesecond coil or the second radiating element via capacitance regardlessof whether current is induced to the second coil as a result of flow ofcurrent through the first radiating element. Therefore, even when theresonant frequency is equal or substantially equal to the anti-resonantfrequency, the second radiating element resonates and contributes to awider bandwidth.

According to a preferred embodiment of the present invention, an antennacoupling element includes a plurality of conductor patterns provided ina plurality of layers laminated via an electrically insulating layer,and a plurality of interlayer connection conductors providing interlayerconnection between predetermined positions of the plurality of conductorpatterns. The plurality of conductor patterns includes a first conductorpattern, a second conductor pattern, a third conductor pattern, and afourth conductor pattern, respectively provided in different layers inorder of a direction of the lamination. The plurality of interlayerconnection conductors includes a first interlayer connection conductorproviding interlayer connection between the first conductor pattern andthe second conductor pattern, and a second interlayer connectionconductor providing interlayer connection between the third conductorpattern and the fourth conductor pattern. The first coil includes thefirst conductor pattern, the second conductor pattern, and the firstinterlayer connection conductor. The second coil includes the thirdconductor pattern, the fourth conductor pattern, and the secondinterlayer connection conductor.

With the above features, a capacitance is generated particularly betweenthe second conductor pattern and the third conductor pattern. Currentflowing through the first coil between the feed circuit and the firstradiating element flows through the second coil or the second radiatingelement via the capacitance regardless of whether current is induced tothe second coil as a result of flow of current through the firstradiating element.

According to a preferred embodiment of the present invention, each ofthe second conductor pattern and the third conductor pattern is longerthan each of the first conductor pattern and the fourth conductorpattern. With these features, the area in which the second conductorpattern and the third conductor pattern face each other increases, sothe capacitance that is generated between the first coil and the secondcoil is significantly increased.

According to a preferred embodiment of the present invention, at leastone of the second conductor pattern and the third conductor patternincludes a capacitance generating conductor pattern that faces in adirection of the lamination to partially generate a capacitance. Withthese features, the capacitance that is generated between the first coiland the second coil is significantly increased.

According to a preferred embodiment of the present invention, the thirdconductor pattern has an extended conductor pattern that extends to anend portion of the electrically insulating layer, and the capacitancegenerating conductor pattern includes the extended conductor pattern anda conductor pattern facing the extended conductor pattern. With thesefeatures, the extended conductor pattern can also be used as one of thecapacitance generating conductor patterns, so further miniaturization ispossible accordingly.

According to a preferred embodiment of the present invention, acapacitance is generated between the first coil and the second coil.With these features, current flowing through the first coil flowsthrough the second coil or the second radiating element via thecapacitance.

An antenna device according to a preferred embodiment of the presentinvention includes an antenna coupling element according to a preferredembodiment of the present invention, a first radiating elementelectrically connected to the first radiating element connection end,and a second radiating element electrically connected to the secondradiating element connection end.

With the above features, even when the resonant frequency of the secondradiating element coincides with the anti-resonant frequency, theresonant characteristics of the second radiating element appear, and awideband antenna device is provided.

An antenna device according to a preferred embodiment of the presentinvention includes a first radiating element, a second radiatingelement, a coupling circuit including a first coupling element and asecond coupling element, the first coupling element being electricallyconnected between the first radiating element and a feed circuit, thesecond coupling element being inductively coupled to the first couplingelement and electrically connected between the second radiating elementand a ground, and a capacitance provided between the first couplingelement and the second coupling element. At an anti-resonant frequencyof the first radiating element, current flows from the first couplingelement to the second coupling element or the second radiating elementvia the capacitance.

With the above features, even when the resonant frequency of the secondradiating element coincides with the anti-resonant frequency, theresonant characteristics of the second radiating element appear, and awideband antenna device is provided.

According to a preferred embodiment of the present invention, the firstcoupling element and the second coupling element are coils coupled toeach other with a magnetic field, and the capacitance is a capacitancethat is generated between the coil that is the first coupling elementand the coil that is the second coupling element. With these features,an induction coupling structure between the first coupling element andthe second coupling element and addition of a capacitance are providedwith a simple configuration.

According to a preferred embodiment of the present invention, at ananti-resonant frequency of the first radiating element, a direction ofcurrent that flows from the first coupling element to the secondcoupling element via the capacitance is a same direction as a directionof current that flows through the second coupling element as a result ofmagnetic field coupling with the first coupling element. With thesefeatures, current flowing through the second coupling element as aresult of magnetic field coupling with the first coupling element andcurrent flowing through the second coupling element from the firstcoupling element via the capacitance enhance each other, and the secondradiating element is driven, so a wider bandwidth is provided by thesecond radiating element.

According to a preferred embodiment of the present invention, acapacitor may be electrically connected between a connection end of thefirst radiating element and a connection end of the second radiatingelement. With these features, a predetermined capacitance can be addedindependently of the configuration of a coupling circuit.

According to a preferred embodiment of the present invention, andelectronic device includes an antenna device according to a preferredembodiment of the present invention, a feed circuit electricallyconnected to the antenna device, and a casing accommodating the feedcircuit, and a portion or all of the first radiating element and thesecond radiating element are defined by a portion of the casing.

With the above features, no electrically conductive member or conductorpattern exclusively for a radiating element needs to be provided, sominiaturization is possible. Even in the electronic device including ametal casing, no shielding is performed by the metal casing.

According to the preferred embodiments of the present invention, antennacoupling elements that each enable effective use of resonance of asecond radiating element by resolving a problem due to anti-resonance ofa first radiating element and that enables a wider bandwidth in a widefrequency band, and antenna devices and electronic devices, eachincluding an antenna coupling element, are provided.

The above and other elements, features, steps, characteristics andadvantages of the present invention will become more apparent from thefollowing detailed description of the preferred embodiments withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an antenna coupling element 30 that isan example of a coupling circuit according to a first preferredembodiment of the present invention.

FIG. 2 is an exploded plan view that shows conductor patterns providedin layers of the antenna coupling element 30.

FIG. 3 is a circuit diagram of the antenna coupling element 30 includingfour coil conductor patterns.

FIG. 4 is an equivalent circuit diagram of an antenna device 100including the antenna coupling element 30, a feed radiating element 11,and a passive radiating element 12.

FIG. 5 is a perspective view of an antenna device 100 according to asecond preferred embodiment of the present invention.

FIG. 6 is a graph that shows the frequency characteristics of theantenna device 100.

FIG. 7 is a perspective view that shows the main structure of anelectronic device 200 according to the second preferred embodiment ofthe present invention.

FIG. 8 is an equivalent circuit diagram of the existing antenna device100 including a feed radiating element and a passive radiating elementcoupled to each other with a magnetic field.

FIG. 9A is a graph that shows the frequency characteristics of anexisting antenna device including a passive radiating element, and FIG.9B is a graph that shows the frequency characteristics of the antennadevice when the resonant frequency of the passive radiating element isdecreased from the state shown in FIG. 9A.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First PreferredEmbodiment

FIG. 1 is a perspective view of an antenna coupling element 30 that isan example of a coupling circuit according to a first preferredembodiment of the present invention. FIG. 2 is an exploded plan viewthat shows conductor patterns provided in layers of the antenna couplingelement 30.

The antenna coupling element 30 of the first preferred embodiment is arectangular parallelepiped or a substantially rectangular parallelepipedchip component that is mounted on a circuit board of an electronicdevice. In FIG. 1, the outer shape of the antenna coupling element 30and the internal structure of the antenna coupling element 30 areseparately shown. The outer shape of the antenna coupling element 30 isrepresented by the alternate long and two short dashed line. A feedcircuit connection terminal PF, a feed radiating element connectionterminal PA, a ground terminal PG, and a passive radiating elementconnection terminal PS are provided on the outer surface of the antennacoupling element 30. The antenna coupling element 30 includes a firstsurface MS1 and a second surface MS2 that is opposite from the firstsurface MS1. In the first preferred embodiment, the first surface MS1 isa mounting surface and faces the circuit board. A directiondiscrimination mark DDM is provided on the second surface MS2 (topsurface) on the opposite side from the first surface MS1 (mountingsurface). The direction discrimination mark DDM is used to detect thedirection of the chip component, for example, when the antenna couplingelement 30 as the chip component is mounted on the circuit board with amounter.

The “feed radiating element” described in preferred embodiments of thepresent invention including the first preferred embodiment correspondsto a “first radiating element”, and the “passive radiating element”corresponds to a “second radiating element”.

A first conductor pattern L11, a second conductor pattern L12, a thirdconductor pattern L21, and a fourth conductor pattern L22 are providedin the antenna coupling element 30. The first conductor pattern L11 andthe second conductor pattern L12 are electrically connected via aninterlayer connection conductor V1. The third conductor pattern L21 andthe fourth conductor pattern L22 are electrically connected via aninterlayer connection conductor V2. In FIG. 1, electrically insulatingbase materials S11, S12, S21, S22 on which the above-described conductorpatterns are provided are separately shown in a direction of lamination.

The feed circuit connection terminal PF and the feed radiating elementconnection terminal PA are terminals to which both ends of a primarycoil (L1 described later) are electrically connected. The passiveradiating element connection terminal PA and the ground terminal PG areterminals to which both ends of a secondary coil (L2 described later)are electrically connected. Although the names of the terminals arenames in the case where the terminals are applied to an antenna device(described later), the names are used here.

As shown in FIG. 2, the first conductor pattern L11 is provided on theelectrically insulating base material S11, the second conductor patternL12 is provided on the electrically insulating base material S12, thethird conductor pattern L21 is provided on the electrically insulatingbase material S21, and the fourth conductor pattern L22 is provided onthe electrically insulating base material S22. As for these coilconductor patterns, the electrically insulating base materials S11, S12,S21, S22 are laminated, and the first conductor pattern L11, the secondconductor pattern L12, the third conductor pattern L21, and the fourthconductor pattern L22 are provided in order from the layer closer to themounting surface. In FIG. 2, the electrically insulating base materialson which the coil conductor patterns are provided are shown. In theantenna coupling element 30 of the first preferred embodiment, aplurality of electrically insulating base materials on which no coilconductor pattern is provided is laminated on each of the lower side ofthe electrically insulating base material S11 and the upper side of theelectrically insulating base material S22.

A first end of the first conductor pattern L11 is electrically connectedto the feed circuit connection terminal PF, and a second end of thefirst conductor pattern L11 is electrically connected to a first end ofthe second conductor pattern L12 via the interlayer connection conductorV1. A second end of the second conductor pattern L12 is electricallyconnected to the feed radiating element connection terminal PA. A firstend of the third conductor pattern L21 is electrically connected to thepassive radiating element connection terminal PS, and a second end ofthe third conductor pattern L21 is electrically connected to a first endof the fourth conductor pattern L22 via the interlayer connectionconductor V2. A second end of the fourth conductor pattern L22 iselectrically connected to the ground terminal PG.

A capacitance generating conductor pattern C11 is provided in a portionof the second conductor pattern L12. A capacitance generating conductorpattern C12 is formed in a portion of the third conductor pattern L21.The capacitance generating conductor pattern C11 of the second conductorpattern L12 and the capacitance generating conductor pattern C12 of thethird conductor pattern L21 face each other in the direction oflamination and define a capacitance at the facing portion.

The capacitance generating conductor pattern C12 of the third conductorpattern L21 is also a portion of an extended conductor pattern from oneend of the third conductor pattern L21 to the passive radiating elementconnection terminal PS. In other words, the extended conductor pattern(capacitance generating conductor pattern C12) and a conductor patternfacing the extended conductor pattern (capacitance generating conductorpattern C11) are capacitance generating conductor patterns.

When the antenna coupling element 30 is made of a resin multilayerboard, the electrically insulating base materials S11, S12, S21, and S22are preferably, for example, liquid crystal polymer (LCP) sheet, and theconductor patterns L11, L12, L21, and L22 are preferably, for example,formed by patterning copper foil. When the antenna coupling element 30is made of a ceramic multilayer board, the electrically insulating basematerials S11, S12, S21, S22 are preferably, for example,low-temperature co-fired ceramics (LTCC), and the conductor patternsL11, L12, L21, L22 are preferably, for example, formed by printingcopper paste.

FIG. 3 is a circuit diagram of the antenna coupling element 30 includingthe four coil conductor patterns. The second conductor pattern L12 andthe first conductor pattern L11 are electrically connected in series anddefine the primary coil L1. Similarly, the fourth conductor pattern L22and the third conductor pattern L21 are electrically connected in seriesand define the secondary coil L2. The primary coil L1 corresponds to a“first coil” and a “first coupling element”. The secondary coil L2corresponds to a “second coil” and a “second coupling element”. Theprimary coil L1 and the secondary coil L2 are coupled to each other witha magnetic field. In FIG. 3, a capacitance that is generated between theprimary coil L1 and the secondary coil L2 is represented by a capacitorC10.

With the above features, the conductor patterns L11, L12, L21, L22overlap all around in plan view and the conductor patterns L11, L12,L21, L22 are closest to each other in the direction of lamination(adjacent to each other in the direction of lamination withoutintervening any other electrically insulating base material), so thecoupling coefficient between the primary coil L1 and the secondary coilL2 is high. Each of the second conductor pattern L12 and the thirdconductor pattern L21 is longer than each of the first conductor patternL11 and the fourth conductor pattern L22. Thus, the area in which thesecond conductor pattern L12 and the third conductor pattern L21 faceeach other is large, so the capacitance that is generated between theprimary coil L1 and the secondary coil L2 is significantly increased.

A winding direction that is routed along a current path from the feedcircuit connection terminal PF to the feed radiating element connectionterminal PA is clockwise in plan view in FIG. 2, while a windingdirection that is routed along a current path from the passive radiatingelement connection terminal PS to the ground terminal PG iscounterclockwise in plan view in FIG. 2. In other words, the windingdirections are opposite to each other.

FIG. 4 is an equivalent circuit diagram of an antenna device 100including the antenna coupling element 30, a feed radiating element 11,and a passive radiating element 12. In FIG. 4, a capacitor C1 thatcorresponds to a parasitic capacitance that is generated in the primarycoil L1 and a capacitor C2 that corresponds to a parasitic capacitancethat is generated in the secondary coil L2 are also shown.

As current is supplied from the feed circuit 1 to the feed radiatingelement 11 via the primary coil L1, current represented by the brokenarrow flows through the secondary coil L2 because of magnetic fieldcoupling (inductive coupling) between the primary coil L1 and thesecondary coil L2. On the other hand, as represented by the solid arrow,current flows through a path (first path) of the feed circuit 1, theprimary coil L1, the capacitor C10, and the secondary coil L2 or a path(second path) of the feed circuit 1, the primary coil L1, the capacitorC10, and the passive radiating element 12.

The passive radiating element 12 is equivalently shown as a circuit inwhich a series circuit of a reactance element and a radiation resistanceis electrically connected between the passive radiating elementconnection terminal PS and a ground. Therefore, on the condition thatthe series circuit is lower in impedance than the secondary coil L2,current flows through the second path.

Current flowing through the primary coil L1 between the feed circuit 1and the feed radiating element 11 flows through the secondary coil L2 orthe passive radiating element 12 via the capacitor C10 even when nocurrent flows through the feed radiating element 11. In other words,even at an anti-resonant frequency of the feed radiating element 11, atwhich no current flows through the secondary coil L2, current flows fromthe primary coil L1 (first coupling element) to the secondary coil L2(second coupling element) or the passive radiating element 12 via thecapacitor C10 (capacitance). For this reason, even when the resonantfrequency of the passive radiating element 12 is equal or substantiallyequal to the anti-resonant frequency, the passive radiating element 12resonates. Therefore, the passive radiating element 12 contributes to awider bandwidth.

When the direction of current (first current) flowing from the primarycoil L1 to the secondary coil L2 via the capacitor C10 is the same asthe direction of current (second current) flowing through the secondarycoil L2 because of magnetic field coupling with the primary coil L1, thefirst current and the second current enhance each other, and the passiveradiating element 12 is driven, so a wider bandwidth is provided by thepassive radiating element 12.

FIG. 1 and FIG. 2 show the example in which the conductor patternlengths, that is, the numbers of turns, of the primary coil L1 andsecondary coil L2 are equal or substantially equal to each other.Alternatively, the conductor pattern lengths, that is, the numbers ofturns, may be determined according to the lengths (antenna lengths) ofthe feed radiating element 11 and passive radiating element 12. Forexample, when a passive radiating element is caused to resonate in alower frequency band than a feed radiating element, the passiveradiating element has a longer antenna length than the feed radiatingelement. In this case, the secondary coil L2 to which the passiveradiating element is electrically connected has a longer conductorpattern length, that is, a greater number of turns, than the primarycoil L1. Thus, an inductance that is added to the passive radiatingelement is increased to significantly decrease the resonant frequencyand significantly improve the capability to drive the passive radiatingelement.

As described above, the feed radiating element 11 is a radiating element(first radiating element) that is supplied with current directly fromthe feed circuit 1 via the primary coil L1. The passive radiatingelement 12 is a radiating element (second radiating element) that issupplied with current indirectly from the feed circuit 1 side throughmagnetic field coupling between the primary coil L1 and the secondarycoil L2.

FIG. 1 and FIG. 2 show the example in which the primary coil L1 includesthe two conductor patterns provided in two layers of a multilayer bodyand the secondary coil L2 includes the two conductor patterns providedin two layers of the multilayer body. However, preferred embodiments ofthe present invention are not limited to this structure. The numbers ofturns of the primary coil L1 and secondary coil L2 are not limited toless than one (not reaching one turn) as shown in FIG. 1 and FIG. 2, andmay be greater than or equal to one turn.

Second Preferred Embodiment

In a second preferred embodiment of the present invention, an example ofan antenna device and an electronic device including the antenna devicewill be described.

FIG. 5 is a perspective view of the antenna device 100 according to thesecond preferred embodiment. The antenna device 100 includes a substrate10, the feed radiating element 11, and the passive radiating element 12.The substrate 10 includes a ground region 10G and a non-ground region10N. A ground conductor pattern expanding in a sheet shape is providedin the ground region 10G. No sheet-shaped ground conductor is providedin the non-ground region 10N.

The feed radiating element 11 and the passive radiating element 12 areprovided in the non-ground region 10N of the substrate 10. In FIG. 5,the feed radiating element 11 and the passive radiating element 12represent only conductor pattern portions.

A main portion of the feed radiating element 11 and a main portion ofthe passive radiating element 12 are conductor patterns provided on theouter surface of a dielectric block or dielectric structure member. Thedielectric block on which the main portions of the feed radiatingelement 11 and passive radiating element 12 are provided in this way ismounted on the substrate 10. The dielectric structure in which the mainportions of the feed radiating element 11 and passive radiating element12 are provided is incorporated as a portion of a casing and iselectrically connected to conductor patterns of the substrate 10.

The feed radiating element 11 is a conductor pattern bent at multipleportions midway from its connection end 11C to its open end 11E.Similarly, the passive radiating element 12 is a conductor pattern bentat multiple portions midway from its connection end 12C to its open end12E.

An antenna coupling element (the antenna coupling element 30 shown inFIG. 1) is mounted on the substrate 10. The antenna coupling element 30is electrically connected to the connection end 11C of the feedradiating element 11 and the connection end 12C of the passive radiatingelement 12. The antenna coupling element 30 is as described in the firstpreferred embodiment. Therefore, even at the anti-resonant frequency ofthe feed radiating element 11, at which no current flows through thesecondary coil L2, current flows from the primary coil L1 (firstcoupling element) to the secondary coil L2 (second coupling element) orthe passive radiating element 12 via the capacitor C10 (capacitance).

FIG. 6 is a graph that shows the frequency characteristics of theantenna device 100. The abscissa axis represents frequency, and theordinate axis represents a return loss (S11) of the antenna device 100,viewed from the feed circuit 1. In FIG. 6, resonant points appear atfrequencies fo, fh, fs. The frequency fo is the fundamental (λ/4)resonant frequency of the feed radiating element 11, and the frequencyfh is the harmonic (3λ/4) resonant frequency of the feed radiatingelement 11. The frequency fs is the resonant frequency of the passiveradiating element 12. In this example, the frequency fs is equal orsubstantially equal to the anti-resonant frequency of the feed radiatingelement 11. However, the characteristics are not as shown as FIG. 9B asan existing example, and the resonant characteristics of the passiveradiating element 12 appear.

In FIG. 6, a frequency band having the frequency fo as a center is usedin communication of, for example, about 800 MHz band and about 900 MHzband of GSM (registered trademark), and a frequency band having thefrequency fh as a center is used in communication of, for example, about1800 MHz band of GSM (registered trademark). The frequency bandsincluding the frequencies fs, fh are used in, for example, reception ofGPS signals and communication of Band 11 and Band 21 of LTE. Accordingto the second preferred embodiment, when the passive radiating element12 and the antenna coupling element 30 are electrically connected, eventhe existing antenna element for communication of, for example, about800 MHz band, about 900 MHz band, and about 1800 MHz band of GSM(registered trademark) can be directly used for reception of GPS signalsand communication of Band 11 and Band 21 of LTE.

FIG. 7 is a perspective view that shows the main structure of anelectronic device 200 according to the second preferred embodiment. Theelectronic device 200 is, for example, a mobile electronic device, andincludes an electrically conductive casing 50 and a resin bezel 51.However, in FIG. 7, the electronic device 200 is shown in a state inwhich one surface of the bezel 51 is open. The substrate 10 shown inFIG. 5 is accommodated in the casing. The non-ground region 10N of thesubstrate 10 shown in FIG. 5 is located at a portion of the bezel (aportion of the casing, not covered with a metal portion).

In the example shown in FIG. 1 to FIG. 4, a current path is provided byusing the capacitance that is generated between the second conductorpattern L12 and the third conductor pattern L21. Alternatively, acapacitor other than the capacitance that is generated between thesecond conductor pattern L12 and the third conductor pattern L21 may beprovided between the feed radiating element connection terminal PA andthe passive radiating element connection terminal PS. For example, anelectrode that defines a capacitor (electrode capacitance generatingconductor pattern) may be provided. A capacitor that is electricallyconnected between the feed radiating element connection terminal PA andthe passive radiating element connection terminal PS may be mountedoutside the antenna coupling element 30 (for example, on the circuitboard).

Antenna devices according to preferred embodiments of the presentinvention are not limited to a transmission purpose and may be used forreception or for transmission and reception. The antenna device alsosimilarly operates even when transmission and reception areinterchanged. The “feed circuit” is not limited to a circuit thatoutputs transmitting power, and, during reception, corresponds to acircuit that inputs a reception signal and amplifies the receptionsignal.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing from the scopeand spirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

What is claimed is:
 1. An antenna coupling element comprising: a firstcoil; a second coil coupled to the first coil; a plurality of conductorpatterns provided in a plurality of layers laminated via an electricallyinsulating layer; and a plurality of interlayer connection conductorsproviding an interlayer connection between predetermined positions ofthe plurality of conductor patterns; wherein a first end of the firstcoil is a feed circuit connection end, a second end of the first coil isa first radiating element connection end, a first end of the second coilis a second radiating element connection end, and a second end of thesecond coil is a ground connection end; a winding direction of anentirety of the first coil that is routed along a current path from thefeed circuit connection end to the first radiating element connectionend and a winding direction of an entirety of the second coil that isrouted along a current path from the second radiating element connectionend to the ground connection end are opposite to each other; theplurality of conductor patterns include a first conductor pattern, asecond conductor pattern, a third conductor pattern, and a fourthconductor pattern, respectively provided in different layers in order ofa direction of the lamination; the plurality of interlayer connectionconductors includes a first interlayer connection conductor providinginterlayer connection between the first conductor pattern and the secondconductor pattern, and a second interlayer connection conductorproviding interlayer connection between the third conductor pattern andthe fourth conductor pattern; the first coil includes the firstconductor pattern, the second conductor pattern, and the firstinterlayer connection conductor; and the second coil includes the thirdconductor pattern, the fourth conductor pattern, and the secondinterlayer connection conductor.
 2. The antenna coupling elementaccording to claim 1, wherein each of the second conductor pattern andthe third conductor pattern has a longer conductor pattern length than aconductor pattern length of each of the first conductor pattern and thefourth conductor pattern.
 3. The antenna coupling element according toclaim 1, wherein at least one of the second conductor pattern and thethird conductor pattern at least partially includes a capacitancegenerating conductor pattern that faces in a direction of the laminationto define a capacitance.
 4. The antenna coupling element according toclaim 3, wherein the third conductor pattern includes an extendedconductor pattern that extends to an end portion of the electricallyinsulating layer, and the capacitance generating conductor patternincludes the extended conductor pattern and a conductor pattern facingthe extended conductor pattern.
 5. The antenna coupling elementaccording to claim 1 wherein a capacitance is defined between the firstcoil and the second coil.
 6. An antenna device comprising: the antennacoupling element according to claim 1; a first radiating elementelectrically connected to the first radiating element connection end;and a second radiating element electrically connected to the secondradiating element connection end.
 7. An electronic device comprising:the antenna device according to claim 6; a feed circuit electricallyconnected to the antenna device; and a casing accommodating the feedcircuit; wherein at least a portion of the first radiating element is aportion of the casing, and at least a portion of the second radiatingelement is a portion of the casing.
 8. The antenna coupling elementaccording to claim 1, wherein the first end of the first coil iselectrically connected to a feed circuit connection terminal provided onan outer surface of the antenna coupling element; the second end of thefirst coil is electrically connected to a first radiating elementconnection terminal provided on the outer surface of the antennacoupling element; the first end of the second coil is electricallyconnected to a second radiating element connection terminal provided onthe outer surface of the antenna coupling element; and the second end ofthe second coil is electrically connected to a ground terminal providedon the outer surface of the antenna coupling element.
 9. The antennadevice according to claim 6, wherein the first radiating element is afeed radiating element and the second radiating element is a passiveradiating element.
 10. The antenna coupling element according to claim1, wherein an electrically insulating base material on which no coilconductor pattern is provided is laminated on a surface of theelectrically insulating layer.
 11. The antenna coupling elementaccording to claim 10, wherein the electrically insulating base materialincludes a liquid crystal polymer (LCP) sheet, and the plurality ofconductor patterns are provided by patterning copper foil.
 12. Theantenna device according to claim 9, wherein current flows through apath of the first radiating element, the first coil, and the secondradiating element only if an impedance of the second radiating elementis lower than an impedance of the second coil.
 13. The antenna couplingelement according to claim 1, wherein at an anti-resonant frequency ofthe first radiating element, current flows from the first coil to thesecond coil or the second radiating element; and the first radiatingelement resonates at λ/2 at the anti-resonant frequency, where λ is awavelength of a propagating frequency.
 14. An antenna device comprising:a first radiating element; a second radiating element; a couplingcircuit including a first coupling element and a second couplingelement, the first coupling element being electrically connected inseries between the first radiating element and a feed circuit, thesecond coupling element being inductively coupled to the first couplingelement and electrically connected between the second radiating elementand a ground; and a capacitance provided between the first couplingelement and the second coupling element; wherein at an anti-resonantfrequency of the first radiating element, the first radiating element isan open circuit when viewed from the feed circuit and current flows fromthe first coupling element to the second coupling element or the secondradiating element via the capacitance; and the first radiating elementresonates at λ/2 at the anti-resonant frequency, where λ is a wavelengthof a propagating frequency.
 15. The antenna device according to claim14, wherein the first coupling element and the second coupling elementare coils coupled to each other with a magnetic field; and thecapacitance is generated between the coil that is the first couplingelement and the coil that is the second coupling element.
 16. Theantenna device according to claim 14, wherein at the anti-resonantfrequency of the first radiating element, a direction of current thatflows from the first coupling element to the second coupling element viathe capacitance is a same direction as a direction of current that flowsthrough the second coupling element as a result of magnetic fieldcoupling with the first coupling element.
 17. The antenna deviceaccording to claim 14, further comprising a capacitor electricallyconnected between a connection end of the first radiating element and aconnection end of the second radiating element.